Plunger for gas lift system with novel skirt

Abstract

A plunger with expandable mating pad elements arrayed circumferentially about the plunger's body sealed to the plunger and biased to expand the plunger assembly's outer circumferential surface toward the inner surface of the tubular within which the plunger assembly is designed to operate. The gaps between the pad elements are minimized by having the adjacent pad elements slidable against each other along two sets of surfaces along essentially the length of the interface between adjacent pad elements, one surface set being approximately axial to the plunger and the other set being approximately radial to the plunger's longitudinal axis, and in this way reducing the available pathway in the gap between adjacent pad elements for fluid to bypass the plunger assembly.

What is claimed is: 
     
       1. A plunger assembly for use in a gas/fluid lift system in a well, comprising:
 a plunger body; 
 a pad subassembly having a plurality of pad elements disposed about the body, each of the pad elements having an outer surface and an inner surface, first and second sides, and top and bottom ends; 
 the pad subassembly biased to move radially outward from the plunger body such that the pad subassembly can expand outwardly from the plunger body for providing an external seal against the interior of the well's tubulars; 
 the first and second sides of the pad elements having engaging means for mating with corresponding engaging means of an adjacent pad element for reducing fluid communication parallel to the plunger body longitudinal axis; 
 wherein the engagement mating means are overlapping mated surfaces between the pads to engage and form slidable slideable seals which are both axial to the plunger body and radial to the plunger body and are continuous along an edge of a joint between adjacent pad elements; 
 the engaging means allowing a radial inner surface of each pad element along a gap between the adjacent pad element to mate with a radial outer surface of the adjacent pad element along an entire edge of the gap; 
 the engaging means being a tabbed portion on the entire first side of each pad element and a notched portion on the entire second side of each pad element, the tabbed portion being mutually engageable with the notched portion of the adjacent pad element along an entire edge of the joint between adjacent pads; 
 the tabbed portion having an outer tongue and an inner tongue, the inner tongue being stepped inward and extending out from the outer tongue; and 
 at least one inner surface of the notched portion of each pad element overlapping with at least one external surface of the tabbed portion of the adjacent pad element, which overlap is maintained even when the pad subassembly is further expanded. 
 
     
     
       2. The plunger assembly of  claim 1 , wherein the inner surface of the notched portion has an internal face above the notch and the external surface of the tabbed portion has a side skirt upper face. 
     
     
       3. The plunger assembly of  claim 2 , wherein the internal face above the notch overlaps the side skirt upper face. 
     
     
       4. The plunger assembly of  claim 1 , wherein the inner surface of the notched portion has a notch internal face and the external surface of the tabbed portion has an inner tongue outer face, wherein the notch internal face overlaps the inner tongue outer face. 
     
     
       5. The plunger assembly of  claim 1 , wherein the inner surface of the notched portion has an internal face above the notch and a notch internal face and the external surface of the tabbed portion has a side skirt upper face and an inner tongue outer face, wherein the internal face above the notch overlaps the side skirt upper face and the notch internal face overlaps the inner tongue outer face. 
     
     
       6. The plunger assembly of  claim 1 , wherein the pad subassembly comprises four pad elements. 
     
     
       7. The plunger assembly of  claim 1 , wherein the pad subassembly is composed of a different composition than the plunger body. 
     
     
       8. The plunger assembly of  claim 1 , wherein the pad elements have a T-shaped configuration. 
     
     
       9. The plunger assembly of  claim 1 , further comprising at least one retaining means which limits the outward radial movement of the pad elements, wherein the retaining means is a retaining ring having a hollow inner surface being adjacent to the top end of the pad elements or being adjacent to the bottom end of the pad elements, wherein the upper or the lower end of the pad elements area skirted so as to engage with the retaining ring and be expandably retained proximate to the plunger body. 
     
     
       10. The plunger assembly of  claim 9 , wherein the retaining means is upper and lower retaining rings having a hollow inner surface, the upper retaining ring being adjacent to the top end of the pad elements and the lower retaining ring being adjacent to the bottom end of the pad elements, wherein the upper and the lower end of the pad elements are skirted, such that the upper end of the pad elements engage with the upper retaining ring and the lower end of the pad elements engage with the lower retaining ring, and where the engagement of each pad element's ends with a retaining ring forms a slidable fit to restrict fluid flow past the retaining ring and pad into a space between the pad and plunger body. 
     
     
       11. The plunger assembly of  claim 1 , further comprising at least one biasing means disposed between the pad elements and the plunger body and biasing the elements outwardly from the plunger body. 
     
     
       12. The plunger assembly of  claim 11 , wherein the biasing means comprises one or more springs. 
     
     
       13. The plunger assembly of  claim 11 , wherein the springs are disposed at an upper and a lower end of each pad element.